Electrical resistor



J. R. BECKWITH ELECTRICAL RESISTOR Jan, 6, 1959 2 Sheets-Sheet 1 Filed March 5, 1957 lNl ENTOR JOHN P. BLICKW/TH BY,

RNE Y Jan. 6, 1959 J R. BECKWITH ELECTRICAL RESISTOR 2 Sheets-Sheet 2 Filed March 5, 1957 //v l/EN TOR JOHN R BECK W/ TH A TTORNEY ELECTRICAL RESISTOR John R. Beckwith, Mexico City, Mexico, assignor to Raytheon Manufacturing Company, Waltham, Mass, a corporation of Delaware Application March 5, 1957, Serial No. 643,983

3 Claims. (Cl. 20155) This invention relates to an electrical control mechanism and more particularly to an improved potentiometer or variable resistor especially useful in electronic apparatus where the chassis on which the control is mounted is at a potential different from that of ground.

It is usual in electronic apparatus to mount controls directly on a metallic chassis and to extend the shafts of such controls through a cabinet enclosing the chassis. In cases where the chassis is grounded, this arrangement is satisfactory. However, in cases where the chassis is hot, i. e., at a potential different from that of ground, the control shaft constitutes a potential shock hazard where the control shaft is usually electrically connected to the chassis. In order to eliminate that shock hazard, it has been customary in the past to provide a separate mounting, insulated from the chassis, for the control device. This prior method successfully eliminates the shock hazard but increases the complexity of assembling the equipment. The present invention eliminates the necessity for providing insulating boards on which to mount the control devices by constructing the control device so that the control shaft is insulated from the remainder of the control assembly. This enables the control device to be mounted on a hot chassis and the control shaft to be extended through the cabinet in the usual way with. complete elimination of the shock hazard.

The novel control device together with its construction and mode of operation will become better under stood with reference to the detailed description below considered in connection with the accompanying drawings wherein:

Fig. 1 is a vertical sectional-view of an assembled control embodying the invention;

Fig. 2 is an exploded view of the assembly shown in Fig. 1 in which the parts are displayed along an axis indicated by the broken line;

Fig. 3 is a vertical sectional view of a species of the invention employing twist tabs; and

Figs. 4, 5, and 6 illustrate certain of the constituent parts used in the species of Fig. 3.

Referring now to Figs. 1 and 2 of the drawings, there is shown a housing 1, fabricated of a ductile metal, such as mild steel, provided at one end with a bearing 2 and at the opposite end with lugs 3. A rear bushing 4, having good insulating properties, is provided with a reduced portion which fits within the bearing 2 of the housing. Aninsulating spacer fits closely within the cavity of the housing and is provided With a central circular opening. A wiper ring 6, provided with internal tabs 7 and having a dependent connector 8 terminating in a terminal lug 9, is secured to the spacer 5 by internal tabs 7 which are forced outward and tightly grip the wall defining the central opening. A rotor 10 made of an insulating material is formed with a pair of lateral notches 11 and a central opening 12. The rotor is mounted on a shaft 13 provided with flats 14 which prevent the rotor from turning relative to the shaft and etfectively key the rotor to the shaft. A Wiper frame 15 is provided with a pair 7 2,867,705 Patented Jan. 6, 1959 of lateral tabs 16 which engage notches 11 of the rotor, so that the frame and the rotor rotate as a unit. The frame 15 is made, preferably, of a resilient material, such as Phosphor bronze, which has good electrical conductivity. The frame, alternatively, may be fabricated of spring steel and plated with an electrical conductor such as silver. Carried by the frame are two pairs of wiper arms, arms 17 and 18 being bent forwardly and the other pair of arms 19 and 24) extending rearwardly. Rearward wiper arms 19 and 20 terminate in contacts 21 and 22, which in the assembled mechanism are forced to bear upon the surface of wiper ring 6. Wiper arms 17 and 18, in a similar manner, are provided with wiper contacts 23 and 24 which bear on resistance element 25 mounted on front plate 26. The resistance element 25 may be constructed of a resistive material, such as carbon, held by a binder on a base, the base in turn being secured to the front plate 26. Other resistance elements can easily be substituted. For example, wire having high resistivity may be wound in a suitable form and secured to the front plate. A pair of terminal lugs 27 are electrically connected to the ends of the resistance element and extend down across the skirt 28 of the front plate. It may be observed, by reference to Fig. 2, that terminal lugs 27 are bent to pass through slots in skirt 28 and that the connections to the ends of resistance element 25 are made through front plate 26 because the upper portions of lugs 27 are on the reverse side of that front plate, whereas the resistance element is on the obverse side. This arrangement insulates the lugs 27 from the housing 1 in the assembled mechanism and enhances the rigidity of those terminals. Notches 29 are formed in the periphery of the front plate 26 at locations corresponding to the locations of the lugs 3 of housing 1. Slots 36) are provided in the front plate 26. A retainer 31 is formed with peripheral tabs 32 which are inserted through the slots 30 and subsequently bent so that the retainer is effectually united with the front plate. To the retainer 31, in turn, is secured a threaded nipple 33 having a shoulder 34 which protrudes through the central opening of retainer 31 and is peened at several locations so that lips 35 have been formed clamping the retainer against a collar 36. As shown in Fig. 1, shaft 13 has a reduced end portion 38 journalled in insulating rear bushing 4. The shaft is additionally supported in nipple 33 which has been lined with an insulator sleeve 37 to electrically isolate and act as a bearing for that shaft. It is apparent that, instead of lining the nipple with an insulator, the nipple itself may be fabricated of an insulating material. in the assembled mechanism front plate 26 is fastened to housing 1 by lugs 3 which are positioned in peripheral notches 29 and then bent to grip the front plate, Inadvertent removal of shaft 13 is prevented by a lock ring 39, disposed between front plate 26 and nipple 33, seated in a groove 40 in the shaft. Front plate 26 is formed with a central aperture, permitting passage of shaft 13, and wiper ring 6 is formed with an aperture of sufficient extent to allow the shaft to pass through it without causing an electrical juncture. Connector 8 of the wiper ring is bent to pass through slots 41 in front plate 26 so that terminal 9projects below skirt 28 in proximity to terminal lugs 2'7.

Upon rotation of control shaft 13, rotor 10, which is keyed to the shaft, and frame 15, which is secured to the rotor, are caused to turn so that wiper contacts 23 and 24, which are in close proximity, are moved across the surface of resistance element 25. Where a potential gradient exists across element 25 as a consequence of a voltage applied between terminal lugs 27, contacts 23 and 24 transmit a potential, determined by their position on the element 25, through contacts 21, 22, which bear upon the surface of Wiper ring 6, to the terminal 9.

The frame is prevented from turning through 360 by positioning conector 8 to intercept arms 17 and 18, thereby delimiting the travel of frame 15. Either frame 15 or connector 8 or both may be insulated at points of interception, if desired, to obviate short circuits.

Figs. 3 to 6 illustrate a species of the invention employing twist tabs 46 in lieu of a threaded nipple 33. Those parts which are identical with their corresponding parts depicted in Figs. 1 and 2 are designated by identical numerals. Housing 45, shown in Fig. 4, is provided with ductile twist tabs 46 and a portion of the housing has been removed to define a recess 47; in all other respects housing 45 is similar to housing 1. Front plate 48, shown in Fig. 5, is provided with peripheral notches 49 permitting tabs 46 to extend therethrough; terminal lugs 59 are positioned on the same face of the front plate as the resistance element and are elec trically connected to the ends of that element; and central aperture 51 of front plate 48 defines a bearing for shaft 13. When assembled, as shown in Fig. 3, removal of the shaft is prevented by lock ring 3-9 disposed in chamber 52 and seated in a groove in the shaft 13. Connector 8 of wiper ring 6 extends across chamber 52 in a position to intercept arms 17 and 18, then is bent downwardly and passes between two insulating members, one of the members being front plate 48 and the other member being an insulating shield 53. As illustrated in Fig. 6, shield 53 is provided with a gap 54 formed by a pair of protuberances 55. Terminal lugs 50 also extend downwardly between those two insulating members. Shield 53 is accommodated in recess 47 of housing and acts to insulate connector 8 and terminal lugs from the housing. The connector 8, which passes through gap 55, and lugs 50 project below the shield 53 to provide electrical connections to movable arms 17 and 18 and to the ends of the resistance element 25. In the species of Fig. 3 shaft 13 is supported by front plate 48 and bushing 4.

It is apparent that the construction delineated herein results in a device which is inexpensive and rugged. Those parts which must be made of insulative materials are simple forms, being either planar or cylindrical. The casing 1 and retainer 31, which are of complex shapes, are formed of a ductile metal, preferably steel. Nipple 33 may be made of brass or steel, metals which are easily machined and of adequate strength. Frame 15, another complex shape, can be fabricated from a variety of suitable resilient metallic materials. All the parts are designed so that assembly is easily accomplished.

The invention is not limited to the particular details of construction or materials described, as equivalents will be apparent to those skilled in the art. It is accordingly desired that the appended claims be given an interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electrical control device comprising a metallic housing having a bearing at one end and being open at the opposite end, an insulating bushing in said bearing, a front plate constructed of an insulative material, an arcuate resistance element secured on one face of said front plate, means fastening said front plate to said casing forming an enclosed chamber with said resistance element therein, a metallic control shaft journalled in said insulating bushing and said front plate whereby said 6 shaft is insulated-from said housing, an insulative rotor keyed to said shaft in said chamber, an electrically conductive frame secured to said rotor, said frame having projecting resilient arms, one of said arms bearing on said resistance element, a conductive ring surrounding said shaft in said chamber, said conductive ring being insulated from said shaft and said housing, another of said arms bearing upon said ring, a connector extending from said ring and positioned to intercept said frame to limit the rotation thereof, and terminal lugs providing electrical connections to said connector and the ends of said resistance element.

2. An electrical control device comprising a metallic housing having a hearing at one end and being open at the opposite end, an insulating bushing in said bearing, a front plate constructed of an insulative material, an arcuate resistance element secured to said front plate, means securing said front plate to said metallic housing forming an enclosed chamber with said resistance element therein, a retainer having deformable tabs, said front plate having slots therein disposed to receive said tabs whereby said retainer is secured to said front plate, a threaded nipple secured to said retainer, an insulating sleeve lining the interior of said nipple, a metallic control shaft supported in said nipple and said insulating bushing, said front plate having an aperture permitting passage of said control shaft, an insulative rotor keyed to said shaft in said chamber, an electrically-conductive frame secured to said rotor, said frame having projecting resilient arms, one of said arms bearing on said resistance element, a conductive ring surrounding said shaft in said chamber, said ring being insulated from said shaft and said housing, another of said resilient arms bearing upon said ring, a connector extending from said ring and positioned to intercept said frame to limit the rotation thereof, and terminal means providing electrical connections to said connector and the ends of said resistance element.

3. An electrical control device comprising a metallic housing having a bearing at one end and being open at the opposite end, said housing having protruding peripheral twist tabs, an insulating bushing disposed in said bearing, a front plate constructed of an insulative material, an arcuate resistance element secured to one surface of said front plate, means securing said front plate to said housing forming an enclosed chamber with said resistance element therein, a metallic control shaft supported by said insulating bushing and by said front plate, an insulative rotor keyed to said shaft in said chamber, an electrically-conductive frame secured to said rotor, said frame having projecting resilient arms, one of said arms having a portion bearing on said resistance element, a conductive ring surrounding said shaft in said chamber, said conductive ring being insulated from said shaft and said housing, another of said arms having a portion bearing upon said ring, a connector extending from said ring and positioned to intercept said frame to limit rotation thereof, terminal lugs providing electrical connections to said connector and the ends of said resistance element, and an insulating member interposed between said terminal lugs and said housing.

References Cited in the file of this patent UNITED STATES PATENTS 

